Tight-tolerance coupling of optical transmission lines between optical connectors, such as optical fibers in optical ferrules and optical waveguides in photonic integrated circuits, is important to reduce coupling loss of optical signals. Especially, single mode coupling loss is highly sensitive to misalignment of optical transmission lines in modularly mating optical connectors. For example, position offset of a small amount (e.g., <2 μm) and tilt offset of a small amount (e.g., <1 deg) can cause significant coupling loss (e.g., >−1 dB). Such misalignment can be caused by mismatch of coefficients of thermal expansion (CTE) among materials used for or around optical transmission lines coupled via modularly mating optical connectors. When a plurality of optical transmission lines are coupled in parallel, the misalignment caused by mismatch of CTE can become larger as every transmission line becomes away from a center of a correspondingly coupled transmission line differently than other coupled transmission lines within an optical ferrule.